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  • 1
    ISSN: 0271-2091
    Keywords: Finite Element ; Quasi-three-dimensional ; Interconnected Aquifer Systmes ; Fluid Mass Balance ; Iterated Frontal Method ; Predictor-Corrector Method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The quasi-three-dimensional equations controlling the groundwater flow in heterogeneous and interconnected aquifer systems are discretized by finite elements, considering also the aquifer branching. A new method for fluid mass balance evaluation based on the equivalent nodal source (E.N.S.) concept allows one to express the balance in conservative terms, and interpret finite element equations as nodal balance equations. The solution of the system is based on the frontal method. Use of substructures limits the frontal increase in correspondence to the aquifer branching. In the steady state, the frontal method is integrated with an iterative solution technique to eliminate the frontal increase caused by the presence of aquitards. It converges very rapidly, using a forcing technique with an automatic parameter definition. In the unsteady case the same scope is achieved using a predictor-corrector procedure which employs the Crank-Nicolson method in the corrector phase.This very stable procedure permits use of fairly long time-steps and concerns the case of source terms depending on piezometry (problem of interaction between water table and river). This method has been tested with several fairly complex cases.
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 3 (1983), S. 493-506 
    ISSN: 0271-2091
    Keywords: Modified ; Dodge ; Algorithm ; Parabolized ; Navier-Stokes ; Computational Fluid Dynamics ; Low Speed Flow ; Channel Flow ; Zebra Algorithm ; Mass Balancing ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A revised version of Dodge's split-velocity method for numerical calculation of compressible duct flow has been developed. The revision incorporates balancing of mass flow rates on each marching step in order to maintain front-to-back continuity during the calculation. The (chequerboard) zebra algorithm is applied to solution of the three-dimensional continuity equation in conservative form. A second-order A-stable linear multistep method is employed in effecting a marching solution of the parabolized momentum equations. A chequerboard iteration is ued to solve the resulting implicit non-linear systems of finite-difference equations which govern stepwise transition. Qualitive agreement with analytical predictions and experimental results has been obtained for some flows with well-known solutions.
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  • 3
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    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 3 (1983), S. 529-542 
    ISSN: 0271-2091
    Keywords: Strongly Rotating ; Incompressible ; Free-surface ; Finite-difference ; Coriolis ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The flow of an incompressible fluid in a rapidly rotating right circular cylinder is considered. A source/sink mass distribution at the lateral wall, which is azimuthally uniform and symmetric across the midplane, causes a deviation from wheel flow. The container is only partially full and the inner free surface is allowed to deviate slightly from the vertical. A finite-difference solution of the full axisymmetric, non-linear governing equations was used to obtain the flow field. A special implicit technique for the Coriolis terms which maintains geostrophy was developed and is described. The results obtained for a low Rossby number flow compare quite favourably with the linearized solution. Results are also presented for a case wherein the non-linear terms are important.
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  • 4
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    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 3 (1983), S. 567-581 
    ISSN: 0271-2091
    Keywords: Advection ; Convection ; Estuary ; Fractional ; Step ; Diffusion ; Dispersion ; Moving ; Co-ordinates Transport ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A successful and economical fractional step algorithm for the convection-dispersion-reaction equation is described. Exact solutions are adopted for the reaction and convection steps, the latter by the introduction of a moving co-ordinate system. The dispersion step uses an optimized finite difference algorithm which specifically accommodates the grid non-uniformity. The excellent performance of the algorithm is confirmed by numerical experiments together with computations of the Fourier response and integrated square error characteristics.
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  • 5
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    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 3 (1983), S. 583-590 
    ISSN: 0271-2091
    Keywords: QUICK ; Finite Difference ; Free Surface Flow ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The spatially third-order accurate QUICK finite difference technique is applied to the solution of the depth-integrated equations of motion for steady, subcritical, free surface flow in a wide, shallow, rectangular channel with and without an abrupt expansion. The conservative, control-volume discretization of the equations of motion and the use of QUICK in approximating required cell and cell face average quantities is discussed. Results presented show that it is possible to obtain stable solutions for advective free surface flows without resorting to implicit numerical smoothing.
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  • 6
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    International Journal for Numerical Methods in Fluids 4 (1984) 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 7
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    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 3 (1983), S. 591-604 
    ISSN: 0271-2091
    Keywords: Shallow Water Equations ; Finite Element Method ; Wave Equation ; Numerical Noise ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Numerical noise has been a problem with finite element solutions to the shallow water equations. Two methods used to reduce the noise level are evaluated, and these results are compared with published results for equal-order interpolations. The two methods are mixed-interpolation (quadratic interpolation for velocity and linear interpolation for sea level) and a spectral form of the wave equation. Whereas mixed interpolation removes the troublesome sea level mode, it can still have considerable noise in velocity. The spectral wave equation is efficient and does not contain the spurious eigenmodes which contribute to high noise levels.
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  • 8
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 1-12 
    ISSN: 0271-2091
    Keywords: Review ; Finite Elements ; Meteorology ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The application of the finite-element method to the simulation of meterological fluid flow problems is reviewed. Early studies were aimed primarily at demonstrating the viability of the method for one- and two-dimensional flows, whereas more recent studies have been aimed at demonstrating the efficiency and viability of the method for more complex three-dimensional simulations. There has also been a shift towards exploiting such models to better understand and predict the underlying meteorological phenomena, rather than restricting attention to the development of the algorithms.
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  • 9
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    International Journal for Numerical Methods in Fluids 3 (1983), S. 605-622 
    ISSN: 0271-2091
    Keywords: Natural ; Convection ; Stream ; Function ; Finite ; Element ; Formulation ; C1 ; Continuity ; Truncated ; Quintic ; Restricted Variational Principle ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A finite element stream function formulation is presented for the solution to the two-dimensional double-glazing problem. Laminar flow with constant properties is considered and the Boussinesq approximation used. A restricted variational principle is used, in conjunction with a triangular finite element of C1 continuity, to discretize the two coupled governing partial differential equations (4th order in stream function and second order in temperature). The resulting non-linear system of equations is solved in a segregated (decoupled) manner by the Newton-Raphson linearizing technique.Results are produced for the standard test case of an upright square cavity. These are for Rayleigh numbers in the range 103-105, with a Prandtl number of 0.71. Comparisons are made with benchmark results presented at the 1981 International Comparison study in Venice. In the discussion of results, emphasis is placed on the variation of local Nusselt number along the isothermal walls, particularly near the corner. This reveals a noticeable source of error in the evaluation of the maximum Nusselt number by lower order discretization methods.
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  • 10
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 105-105 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 11
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    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 4 (1984), S. 147-158 
    ISSN: 0271-2091
    Keywords: Finite Element ; Incompressible Flow ; Pressure-specification-point ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The discontinuity of a finite-element pressure field that is sometimes present in the neighbourhood of the pressure-specification-point is shown to arise either from round-off, or from mistakes in modelling. The implications of this are considered. In particular it restricts grid refinement near the pressure-specification-point. The analysis can be extended to finite-difference calculations, and to other fields governed by equations similar to Poisson's equation.
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  • 12
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    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 4 (1984), S. 109-125 
    ISSN: 0271-2091
    Keywords: Finite elements ; Navier-Stokes ; Vorticity-stream function ; Time-dependent ; flows ; Boundary conditions ; Incompressible viscous flows ; Two-dimensional flows ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A new finite element method for solving the time-dependent incompressible Navier-Stokes equations with general boundary conditions is presented. The two second-order partial differential equations for the vorticity and the stream function are factorized, apart from the non-linear advection term, by eliminating the coupling due to the double specification on the stream function at (a part of) the boundary. This is achieved by reducing the no-slip boundary conditions to projection integral conditions for the vorticity field and by evaluating the relevant quantities involved according to an extension of the method of Glowinski and Pironneau for the biharmonic problem. Time integration schemes and iterative algorithms are introduced which require the solution only of banded linear systems of symmetric type. The proposed finite element formulation is compared with its finite difference equivalent by means of a few numerical examples. The results obtained using 4-noded bilinear elements provide an illustration of the superiority of the finite element based spatial discretization.
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  • 13
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    International Journal for Numerical Methods in Fluids 4 (1984) 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 14
    ISSN: 0271-2091
    Keywords: Polymer Flows ; Non-Newtonian ; Moving Boundary ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Recent progress in the simulation of polymeric flows of two key problems in the injection moulding process, carried out by a team at Cornell University, is briefly described. For the filling of cooled thin cavities, the fluid is characterized by a power-law viscosity with exponential temperature dependence, and interaction between the transient thermal boundary-layer and the core flow in a domain with moving boundary is essential. The earlier procedure of Hieber and Shen is modified in two aspects: a boundary-integral formulation replaces the finite-element treatment of the pressure, and an ‘energy integral’ approach is used for the transient temperature. The second problem is the steady visco-elastic flow in the juncture region where sudden changes of the geometry and large strain rates occur. The constitutive equation is postulated according to the Leonov model. The main features in the numerical implementation are: integration along a streamline to determine the elastic deformation tensors for a given velocity field, and finite-element treatment (in time-dependent form) of the pressure and fields for given stresses. In an example where the contraction ratio is 7:1, results for nominal Deborah number exceeding 100 show no numerical instability. (However, for this problem, the true Weissenberg number, i.e. the ratio of local first-normal-stress difference to shear stress turns out to be generally O(10).) The predictions also correlate very well with experimental birefringence measurements.
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  • 15
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 303-319 
    ISSN: 0271-2091
    Keywords: Finite Element ; Turbulent Flow ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Although the finite-element (FE) method has been successful in analysing complex laminar flows, a number of difficulties can arise when two-equation turbulence models (e.g. the k-∊ model) are incorporated. This work describes a particular FE discretization of the k-∊ model and reports its performance in recirculating flow. Severe problems encountered in attempts to obtain convergence of the numerical scheme are isolated and analysed, and methods by which the problems can be overcome are suggested.Insight gained in this work has enabled a practical turbulent flow FE code to be constructed which is robust and efficient. This code is the subject of a further paper.
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  • 16
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 321-336 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Incorporation of the k-∊ turbulence model into Galerkin finite-element fluid-flow codes (which, unlike upwind finite-difference codes, have no artificial damping) can lead to severe iterative convergence difficulties. This paper introduces an alternative turbulence model (the q-f model) and an associated finite-element discretization method which are designed to overcome these problems. The new model forms the basis of a finite-element fluid-flow code which is robust and efficient. Furthermore, it is demonstrated on a practical example that the code can give good agreement with experiment on fairly coarse meshes.
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  • 17
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 399-419 
    ISSN: 0271-2091
    Keywords: Laminar Boundary Layers ; Finite Element Method ; Finite Difference Method ; Spectral Method Convergence ; Computational Efficiency ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The Dorodnitsyn boundary later formulation is given a finite element interpretation and found to generate very accurate and economical solutions when combined with an implicit, non-iterative marching scheme in the downstream direction. The algorithm is of order (Δ2u, Δx) whether linear or quadratic elements are used across the boundary layer. Solutions are compared with a Dorodnitsyn spectral formulation and a conventional finite difference formulation for three Falkner-Skan pressure gradient cases and the flow over a circular cylinder. With quadratic elements the Dorodnitsyn finite element formulation is approximately five times more efficient than the conventional finite difference formulation.
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  • 18
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 421-439 
    ISSN: 0271-2091
    Keywords: Laminar Flow ; Turbulent Flow ; Compressible Flow ; Separation ; Time-split Method ; Finite Element Method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The time-split finite element method is extended to compute laminar and turbulent flows with and without separation. The examples considered are the flows past trailing edges of a flat plate and a backward-facing step. Eddy viscosity models are used to represent effects of turbulence. It is found that the time-split method produces results in agreement with previous experimental and computational results. The eddy viscosity models employed are found to give accurate predictions in all regions of flow except downstream of reattachment.
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  • 19
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 441-457 
    ISSN: 0271-2091
    Keywords: Finite Element Method ; Dip Coating ; Newtonian Fluid ; Free Surface ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A finite element simulation of the dip coating process based on a discretization of the continuum with discontinuous pressure elements is presented. The algorithm computes the flow field from natural boundary conditions while an extra condition provided by the existence of free surface is employed to displace the meniscus location towards the actual position. The process is iterative and uses a pseudo-time stepping technique coupled to a cubic spline fitting of the free surface. Numerical predictions exhibit good agreement with experimental data for Newtonian fluids in the case of flat plate dip coating as well as in the case of wire dip coating.
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  • 20
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 459-475 
    ISSN: 0271-2091
    Keywords: Augmented Lagrangian ; Finite Element Method ; Dip Coating ; Non-Newtonian Fluids ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: We apply in this paper the augmented Lagrangian method to the study of various non-Newtonian fluid flow problems, and in particular the dip coating process. We only present in this second part the treatment specific to the non-linearities involved in the constitutive equations, the first part having largely been concerned with the general description of the approximation used.Two rheological models illustrating different rheological behaviours are used to simulate dip coating process: the Carreau-A model for shear-thinning properties of the viscosity and a truncated second-order model for a Newtonian behaviour in viscosity with elastic properties.Numerical predictions show a very good agreement with experimental data for the second-order model. The discrepancy observed in the other case can be explained qualitatively by the elastic properties exhibited by the shear-thinning fluids used: this elasticity is not taken into account in the Carreau-A model.
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  • 21
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 667-683 
    ISSN: 0271-2091
    Keywords: Rotating Flow ; Finite Differences ; Numerical Stability ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A computer program has been developed to predict laminar source-sink flow in a rotating cylindrical cavity. Although the program is based on a standard finite difference technique for recirculating flow, it incorporates two novel features. Step changes in grid size are employed to obtain sufficient resolution in the boundary layers and special treatment is given to the solution of the pressure correction equations, in the ‘SIMPLE’ algorithm, in order to improve the convergence properties of the method. Results are presented both for the flow in an infinite rotating cylindrical annulus and a finite rotating cylindrical cavity, with the inner cylindrical surface acting as a uniform source and the outer cylinder as a sink. These show good agreement with existing analytical solutions and illustrate some of the problems associated with the computation of rapidly rotating flows.
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  • 22
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 685-699 
    ISSN: 0271-2091
    Keywords: Stokes Flows ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A family of simple Stokes flows involving sliding surfaces adjacent to surfaces at rest is considered. Principally, two specific flow configurations are investigated: (i) that arising when parts of the boundary of an infinitely long circular cylinder are rotating about the axis while other parts of the boundary are at rest, and (ii) the flow produced when a cap of a sphere is held at rest while the remainder of the sphere rotates about the symmetry axis. In each case computer plots of streamlines or constant velocity lines are presented to give a general impression of the resulting flow pattern.
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  • 23
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 708-708 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 24
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 709-709 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 25
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 765-780 
    ISSN: 0271-2091
    Keywords: Diffraction ; Hydrodynamics ; Ocean Engineering ; Underwater Structures ; Wave Forces ; Offshore Structures ; Velocity Potential ; Boundary Elements ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The fluid forces resulting from wave interaction with large submerged structures may be calculated using numerical procedures based on the solution of the associated boundary-value problem. In this paper, the analysis of wave interaction with a fixed submerged object of arbitrary cross-section and infinite length using a two-dimensional boundary value formation based on linear diffraction theory is summarized. Subsequently, the application of the boundary element method to obtain a solution is presented. The numerical considerations are emphasized with particular reference to computational efficiency.Numerical results are presented in the form of dimensionless wave force plots for various structural shapes. In the case of a bottom-seated half cylinder, for which there exists a closed-form solution, comparisons are made between results generated using both boundary element and equivalent finite element approaches. In the case of a submerged cylinder, comparisons are made between boundary element derived values and experimental results. The boundary element results compare well with both the closed-form solution and the experimental values.
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  • 26
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    International Journal for Numerical Methods in Fluids 4 (1984) 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 27
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 931-947 
    ISSN: 0271-2091
    Keywords: Two-layer Flow ; Two-step Scheme ; Selective Lumping Method ; Ishikari Bay ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A finite element method for the analysis of two-layer density flows is presented in this paper. The standard Galerkin method based on linear interpolation functions is used to yield discrete spatial variables. For numerical integration in time, an explicit two-step selective lumping method is used. Here it is applied to a flow analysis of Ishikari Bay, at the mouth of Ishikari River. This case demonstrates a procedure that yields a numerically stable solution.
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  • 28
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 949-969 
    ISSN: 0271-2091
    Keywords: Navier-Stokes ; Discrete Fourier Transform ; Finite Difference ; Short Convolutions ; No-slip Boundary Condition ; Far Field Condition ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A mixed discrete Fourier transform-Finite difference algorithm is developed and used for the calculation of rapidly changing viscous fluid flows past a circular cylinder. The numerical approach has been designed to overcome certain difficulties arising for high Reynolds number simulations. The foremost advantage of the technique lies in its fast calculations of the convolution sums portraying the convective terms of the governing equations. Third-order spatial discretizations and fourth-order time marching are implemented.New schemes are proposed for the boundary conditions at the solid wall and at large distances. The techniques are tested on a case study with other schemes (summarized by Roache1) in order to obtain an optimal choice. Definite indications on the stability and accuracy of boundary condition schemes are achieved. Support for the statement of dominant importance of boundary conditions is also given.A comparison of computational results with experimental data is presented for the case study of the flow past an impulsively started cylinder at Reynolds number 20.The time development of the symmetrical zone of recirculation, which is formed at an early stage of the flow, has been studied for 300 ≤ Re ≤ 9500 by means of the proposed algorithm. Computational results, comparisons with experimental data2 and discussion of upper limits of validity of the procedure will be presented in a companion paper.
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  • 29
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 997-998 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 30
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 999-999 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 31
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 989-996 
    ISSN: 0271-2091
    Keywords: Galerkin ; Spline ; Stability ; Disk ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The perturbation equations which characterize the stability of flow over a rotating infinite disk are derived via strict order of magnitude analysis. These equations contain viscous terms not considered by Stuart,1 curvature and Coriolis terms not considered by Brown,2 and axial velocity terms not considered by Kobayashi et al.3 The strategy for reducing the problem to an algebraic system is Galerkin's method with B-spline discretization. In comparison with the Poiseuille flow solutions of Orszag,4 the method is shown to perform well without placing undue demands on computing capability. Critical values of Reynolds number, wave length, vortex orientation and number of spiral vortices calculated by the present method compare favourably with experimental data of Kobayashi et al.
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  • 32
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    International Journal for Numerical Methods in Fluids 4 (1984), S. 1001-1012 
    ISSN: 0271-2091
    Keywords: Compressible Fluid Flow ; Numerical Analysis ; Pressure Method ; von Kármán Vortex Street ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this paper the pressure method for incompressible fluid flow simulation is extended and applied to the numerical simulation of compressible fluid flow. The governing equations, obtained from the physical principles of conservation of momentum, mass and energy, are first studied from a characteristic point of view. Then they are discretized with a semi-implicit finite difference technique in such a fashion that stability is achieved independently of the speed of sound. The resulting algorithm is fast, accurate and particularly efficient in subsonic flow calculations. As an example, the computer simulation of the von Kármán vortex street is described and discussed.
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  • 33
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 319-334 
    ISSN: 0271-2091
    Keywords: Chemically reactive flows ; Finite element analysis ; Polymeric fluids ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: We consider steady state and time-dependent flows of chemically reactive polymeric systems in two-dimensional geometries. A numerical simulation tool is proposed for predicting the evolution of the macroscopic velocity, temperature, stress and species concentration fields in such flows. We formulate a general mathematical model on the basis of the first principles of continuum mechanics, which includes a description of the non-liner coupling between kinematics, heat transfer and chemical kinetics. The resulting set of non-linear partial differential equations is solved numerically by means of appropriate finite element techniques. We have implemented the resulting numerical model in the general-purpose POLYFLOWR software developed in Louvain-la-Neuve, Belgium. Simulation results for various steady state and time-dependent reactive flows are reported.
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  • 34
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 337-339 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 35
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 341-361 
    ISSN: 0271-2091
    Keywords: Navier-Stokes ; unsteady ; composite multigrid ; incompressible ; non-staggered grid ; semi-implicit ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A time-accurate, finite volume method for solving the three-dimensional, incompressible Navier-Stokes equations on a composite grid with arbitrary subgrid overlapping is presented. The governing equations are written in a non-orthogonal curvilinear co-ordinate system and are discretized on a non-staggered grid. A semi-implicit, fractional step method with approximate factorization is employed for time advancement. Multigrid combined with intergrid iteration is used to solve the pressure Poisson equation. Inter-grid communication is facilitated by an iterative boundary velocity scheme which ensures that the governing equations are well-posed on each subdomain. Mass conservation on each subdomain is preserved by using a mass imbalance correction scheme which is secondorder-accurate. Three test cases are used to demonstrate the method's consistency, accuracy and efficiency.
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  • 36
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 393-414 
    ISSN: 0271-2091
    Keywords: shallow water equations ; spectral element ; implicit scheme ; GMRES solver ; staggered mesh ; North Atlantic ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A staggered spectral element model for the solution of the oceanic shallow water equations is presented. We introduce and compare both an implicit and an explicit time integration scheme. The former splits the equations with the operator-integration factor method and solves the resulting algebraic system with generalized minimum residual (GMRES) iterations. Comparison of the two schemes shows the performance of the implicit scheme to lag that of the explicit scheme because of the unpreconditioned implementation of GMRES. The explicit code is successfully applied to various geophysical flows in idealized and realistic basins, notably to the wind-driven circulation in the North Atlantic Ocean. The last experiment reveals the geometric versatility of the spectral element method and the effectiveness of the staggering in eliminating sprious pressure modes when the flow is nearly non-divergent.
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  • 37
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 597-598 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 38
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    International Journal for Numerical Methods in Fluids 20 (1995), S. iii 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 39
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 459-468 
    ISSN: 0271-2091
    Keywords: heat transfer ; turbulent flow ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The accurate modelling of heat transfer to turbulent flow and the prediction of the temperature distribution in the flow remain one of the problem areas of numerical simulations. Traditional turbulence closure models, like the k-ε model, effectively only increase the viscosity of the fluid and introduce wall functions close to boundaries to obtain the correct velocity distribution. These turbulence models do not model the small-scale mixing that occurs in turbulent flow. When solving the energy equation these small-scale mixings dominate the heat transfer rate at the boundaries as well as the temperature distribution in the flow. This paper outlines a revised method, based on the k-ε turbulence model, that can be used to predict heat transfer in turbulent flow. A single turbulent conductivity term is introduced that can be used over the complete flow field including the boundaries. A detailed description of the mathematical model and boundary conditions used for the turbulence model are included in the paper. The effective turbulent conductivity method was evaluated in several finite difference simulations of water flowing through a smooth pipe while being heated. Simulation and verification were performed over a range of Reynolds numbers. Verification of the model is accomplished by comparing the numerically predicted centre temperature of the fluid as well as the heat flux to the fluid to measured temperatures in a similar pipe. From these results it is concluded that the revised turbulent conductivity model holds great potential to obtain accurate simulated heat transfer rates for general applications.
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  • 40
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 541-557 
    ISSN: 0271-2091
    Keywords: electromagnetic induction heating ; inverse method ; finite element ; coupled fields ; experiment simulation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The induction heating model described herein couples the standard heat conduction equation with electro-magnetic proximity-skin equations. An Inverse Finite Element procedure, which is based on prior deterministic and probabilistic concepts, has been designed to solve the inherent inverse equation model with respect to the unknown coil current parameter. Simulated experiments using different noises in the input data have been performed in order to determine their influence on the estimated parameter. The IFEM has shown its capability to predict the optimal location for the temperature sensors, together with their numbers, consistently with a pre-specified estimate accuracy. Specifically, only one temperature sensor, located in the middle of the two turns of the coil, results to be sufficient to estimate the unknown parameter to a satisfactory accuracy degree. This, may significantly help to design optimal experiments.
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  • 41
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 507-522 
    ISSN: 0271-2091
    Keywords: radiative ignition ; pyrolysing solid fuels ; coal ; numerical model ; numerical method of lines ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A numerical model of radiative ignition of pyrolysing solid fuels is developed. The model is one-dimensional and transient. The following mechanisms are simultaneously accounted for: (i) the surface heat and mass transport, (ii) the surface oxidation chemical reaction, (iii) the in-depth pyrolysis, (iv) the gas-phase heating by absorption of the radiation and by heat conduction/convection from the solid surface, and (v) the gas-phase chemical reaction. The solutions are obtained numerically with the method of lines. Using lignite and bituminous coal for the simulations, the results confirm that the pyrolysis products absorb a significant amount of the external radiation. Predictions of the ignition times show that both the surface ignition time and the gas-phase ignition time decrease rapidly with increasing radiation intensities. A good agreement between predictions and experiments is obtained.A sensitivity analysis is also carried out with the key kinetic parameters. This analysis establishes an upper limit for surface and pyrolysis activation energies and a lower limit for gas-phase activation energy. Within these limits, the radiative ignition of coals appears as an integration of two consecutive ignition modes: the surface ignition occurs first, which is then followed by the gas-phase ignition. Beyond these limits, the single gas-phase ignition mode is the only ignition mode to prevail.
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  • 42
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 559-572 
    ISSN: 0271-2091
    Keywords: melting ; natural convection ; body-fitted co-ordinates ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A numerical study of natural convection melting of a phase change material within an isothermal vertical cylinder was conducted. The governing conservation equations are formulated in terms of a stream function, vorticity and temperature. Body-fitted co-ordinates are employed for tracking the irregular shape of the timewise changing solid-liquid phase front. Results show that the convective flow patterns and time evolution of the phase front, resulting from simultaneous bottom, side and top heating, are far more complicated than those for the melting from a single isothermal boundary. The heat transfer rate at the top surface is found to decrease monotonically to zero as convection is fully developed in the melt. The highest heat transfer rates are observed at the bottom surface where Bénard convective cells develop. Due to the convective motion of the melt along the vertical heated wall, the onset of Bénard convection occurs at a much earlier time than that for the case of melting within a cylinder heated from below.
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  • 43
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    International Journal for Numerical Methods in Fluids 20 (1995) 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 44
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 641-648 
    ISSN: 0271-2091
    Keywords: impinging jet ; uniform suction ; turbulence model ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The paper presents numerical predictions of a turbulent axisymmetric jet impinging onto a porous plate, based on a finite volume method of solving the Navier-Stokes equations for an incompressible air jet with the K-ε turbulence model. The velocity and pressure terms of the momentum equations are solved by the SIMPLE (semi-implicit method for pressure-linked equation) method. In this study, non-uniform staggered grids are used. The parameters of interest include the nozzle-to-wall distance and the suction velocity. The results of the present calculations are compared with available data reported in the literature. It is found that suction effects reduce the boundary layer thickness and increase the velocity gradient near the wall.
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  • 45
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    International Journal for Numerical Methods in Fluids 20 (1995) 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 46
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 1153-1161 
    ISSN: 0271-2091
    Keywords: finite element ; arterial flow ; magnetic field ; co-ordinate transformation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A finite element solution of the Navier-Stokes equations for steady flow under the magnetic effect through a double-branched two-dimensional section of a three-dimensional model of the canine aorta is discussed. The numerical scheme involves transforming the physical co-ordinates to a curvilinear boundary-fitted co-ordinate system. The shear stress at the wall is calculated for a Reynolds number of 1000 with the branch-to-main aortic flow rate ratio as a parameter. The results are compared with earlier works involving experimental data and found to be in reasonable qualitative agreement. The steady flow, shear stress and branch flow under the effect of a magnetic field have been discussed in detail.
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  • 47
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 1179-1197 
    ISSN: 0271-2091
    Keywords: adaptive grids ; equidistribution ; compressible viscous aerodynamics ; CFD modelling ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A technique is described for the adaptation of a structured control volume mesh during the iterative solution process of the Navier-Stokes equations. The scalar equidistribution method is adopted, in conjunction with a Laplace-like grid solver to make a curvilinear body-fitted grid sensitive to local flow gradients. Hence, whilst the total number of grid nodes remains constant during a computation, their relative position is continuously adjusted to promote clustering of cells in regions where gradients are high. The focus of this work is in compressible aerodynamics, where such clustering would be desirable in regions containing shocks but also in boundary layers. The technique is three-dimensional and operates in a series of user-defined grid subdomains or patches. These patches act as reference frames within which grid activity takes place. Bi-cubic splines are extensively used to define the aerodynamic surfaces forming the calculation boundaries and to ensure that grid movement does not compromise surface integrity. The technique is applied to aerofoils, wing surfaces, transonic ducts and nozzles and a supersonic wedge cascade. Significant sharpening of both normal and oblique shock discontinuities is demonstrated over static grid simulations and with fewer overall grid nodes. The technique is successful in both inviscid and viscous (turbulent) simulations.
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  • 48
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 1215-1236 
    ISSN: 0271-2091
    Keywords: square obstruction ; channel flow ; vortex shedding ; sliding walls ; numerical calculation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Results are presented for the unsteady, two-dimensional flow and heat transfer due to a square obstruction of diameter d located asymmetrically between the parallel sliding walls of a channel with length-to-height ratio W/H = 6·44. Analysis is based on the numerical solution of spatially and temporally second-order accurate finite difference approximations of the transport equations expressed in curvilinear co-ordinates. Laminar, constant property flow is assumed for obstruction configurations in which the blockage ratio is d/H = 0·192, the nearest-wall distances are g/d = 0·2, 0·5 and 1, the orientation angles are α=0°, 10° and 20° and the Reynolds numbers are Re=100, 500, and 1000. Preparatory testing of the numerical procedure was performed for a variety of documented flows to verify its physiconumerical accuracy and obtain estimates of the residual grid-dependent uncertainties in the variables calculated. Heat transfer, drag and lift coefficients and Strouhal numbers for the present flow were finally calculated to within 4%-7% of their grid-dependent values using non-uniformly spaced grids consisting of (x=99, y=55) nodes. Above a critical value of the Reynolds number, which depends on the geometrical parameters, the flow is characterized by alternate vortex shedding from the obstruction top and bottom surfaces. Streamline, vorticity and particle streakline plots provide qualitative impressions of the unsteady vortical flow. Especially noteworthy are the extremes in the lift coefficient which ranges from large positive values for an obstruction with g/d=0·2 and α=10° to negative values for one with g/d=0·5 and α=0°. Both the drag and lift coefficients as well as the Strouhal number exhibit non-monotonic variations with respect to the parameters explored. Asymmetries in the obstruction location and orientation account for relatively large vortex-induced periodic variations in heat transfer, especially along the wall nearest the obstruction. Notable differences are also predicted for the heat transfer coefficients of the individual obstruction surfaces as a function of the orientation angle.
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 1293-1314 
    ISSN: 0271-2091
    Keywords: chemical reactors ; annular liquid jets ; grid generation ; mass absorption ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A numerical study of Hopf bifuractions in annular liquid jets with mass transfer is presented. The study is based on the asymptotic equations which govern the dynamics of inviscid, incompressible, thin, annular liquid jets and on equilibrium conditions for mass transfer at the jet's inner and outer interfaces. It is shown that the amplitude of the time-periodic motion that results from the Hopf bifurcation increases whereas its frequency decreases as the solubility ratio is increased.
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  • 50
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 1363-1380 
    ISSN: 0271-2091
    Keywords: volume-of-fluid ; free surface flows ; interface advection ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A numerical technique is developed for the simulation of free surface flows and interfaces. This technique combines the strength on the finite element method (FEM) in calculating the field variables for a deforming boundary and the versatility of the volume-of-fluid (VOF) technique in advection of the fluid interfaces. The advantage of the VOF technique is that it allows the simulation of interfaces with large deformations, including surface merging and breaking. However, its disadantage is that is solving the flow equations, it cannot resolve interfaces smaller than the cell size, since information on the subgrid scale is lost. Therefore the accuracy of the interface reconstruction and the treatment of the boundary conditions (i.e. viscous stresses and surface tension forces) become grid-size-dependent. On the other hand, the FEM with deforming interface mesh allows accurate implementation of the boundary conditions, but it cannot handle large surface deformations occurring in breaking and merging of liquid regions. Combining the two methods into a hybrid FEM-VOF method eliminates the major shortcomings of both. The outcome is a technique which can handle large surface deformations with accurate treatment of the boundary conditions. For illustration, two computational examples are presented, namely the instability and break-up of a capillary jet and the coalescence collision of two liquid drops.
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  • 51
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 671-693 
    ISSN: 0271-2091
    Keywords: airfoil ; artificial viscosity ; upwinding ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The numerical solution of the compressible Euler and Navier-Stokes equations in primitive variables form requires the use of artificial viscosity or upwinding. Methods that are first-order-accurate are too dissipative and reduce the effective Reynolds number substantially unless a very fine grid is used. A first-order finite element method for the solution of the Euler and Navier-Stokes equations can be constructed by adding Laplacians of the primitive variables to the governing equations. Second-order schemes may require a fourth-order dissipation and higher-order elements. A finite element approach is proposed in which the fourth-order dissipation is recast as the difference of two Laplacian operators, allowing the use of bilinear elements. The Laplacians of the primitive variables of the first-order scheme are thus balanced by additional terms obtained from the governing equations themselves, tensor identities or other forms of nodal averaging. To demonstrate formally the accuracy of this scheme, an exact solution is introduced which satisfies the continuity equation identically and the momentum equations through forcing functions. The solutions of several transonic and supersonic inviscid and laminar viscous test cases are also presented and compared to other available numerical data.
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 743-776 
    ISSN: 0271-2091
    Keywords: computational aerodynamics ; shock capturing ; positive schemes ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A unified theory of non-oscillatory finite volume schemes for both structured and unstructured meshes is developed in two parts. In the first part, a theory of local extremum diminishing (LED) and essentially local extremum diminishing (ELED) schemes is developed for scalar conservation laws. This leads to symmetric and upstream limited positive (SLIP and USLIP) schemes which can be formulated on either structured or unstructured meshes. The second part examines the application of similar ideas to the treatment of systems of conservation laws. An analysis of discrete shock structure leads to conditions on the numerical flux such that stationary discrete shocks can contain a single interior point. The simplest formulation which meets these conditions is a convective upwind and split pressure (CUSP) scheme, in which the coefficient of the pressure differences is fully determined by the coefficient of convective diffusion. Numerical results are presented which confirm the properties of these schemes.
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  • 53
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 803-817 
    ISSN: 0271-2091
    Keywords: unstructured grids ; finite element ; turbulence ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: An unstructured finite element method is presented for calculation of turbulent flow fields about aerospace configurations. Algebraic, one-equation, and two-equation turbulence models are implemented and compared. A new procedure for implementing an unstructured algebraic model without an auxiliary structured grid is presented. The overall procedure is applied to simulation of flow about launch vehicle configurations. The turbulence models are evaluated for calculation of flow fields about a forebody with shock induced separation. For this case. the one-equation model gives better predictions. An inviscid flow field about a complete launch vehicle with multiple boosters is also evaluated to demonstrate the overall procedure.
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 853-868 
    ISSN: 0271-2091
    Keywords: numerical schemes ; non-linear hyperbolic systems ; Reimann solvers ; adaptive meshes ; unsteady flows ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper discusses the different sources of non-physical entropy production which occur in the numerical resolution of the Euler equations for compressible inviscid flow and proposes several ways of correcting these effects. In particular a hybrid corrected centred, augmented by an accurate upwind scheme near singular boundaries is proposed which satisfies the mathematical entropy condition, and which solves the flow accurately within regions near non-smooth boundaries of the computational domain. A coupled new dynamic auto-adaptive mesh algorithm which produces highly accurate solutions is also introduced. This algorithm is non-hierarchical. i.e. it does not depend on a fixed background mesh, which allows structural and geometrical changes and generates extremely precise discretizations for steady and unsteady flow.
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  • 55
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 915-934 
    ISSN: 0271-2091
    Keywords: optimum design ; mesh adaptivity ; adaptive remeshing ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper presents a methodology for solving shape optimization problems in the context of fluid flow problems including adaptive remeshing. The method is based on the computation of the sensitivities of the geometrical design parameters, the mesh, the flow variables and the error estimator to project the refinement parameters from one design to the next. This sensitivity analysis is described for the incompressible potential equations and the Euler equations. The efficiency of the proposed method is checked by means of two 2D inverse problems.
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 989-1001 
    ISSN: 0271-2091
    Keywords: streamline diffusion ; finite element ; Lagrangian method ; space-time discretization ; 3D flow ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this paper we describe a space-time finite element method, with elements aligned along the computed characteristics in space-time, for the computation of incompressible free surface flows in three dimensions.
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  • 57
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 443-458 
    ISSN: 0271-2091
    Keywords: finite elements ; advection-diffusion ; diffusion errors ; dispersion errors ; stability ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Various finite element schemes of the Bubnov-Galerkin and Taylor-Galerkin types are analysed to obtain the expressions of truncation errors. This way, dispersion errors in the transient, and diffusion errors both in the transient and in the steady state, are identified. Then, with reference to the transient advection-diffusion equation, stability limits are determined by means of a general von Neumann procedure. Finally, the operational equivalence between Taylor-Galerkin methods, utilized for pseudo-transient calculations, and Petrov-Galerkin methods, derived for the steady state forms of the advection-diffusion equation, is illustrated. Theoretical conclusions are supported by the results of numerical experiments.
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  • 58
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 469-492 
    ISSN: 0271-2091
    Keywords: boundary layer ; heat transfer ; turbulence ; CFD ; finite elements ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper presents an efficient finite element method for solving the unsteady Navier-Stokes equations for turbulent incompressible flow coupled with thermal problems. This method has been implemented in the N3S code, developed at Electricité de France. The time discretization is first described. We precise then the Chorin and the ‘projected Uzawa’ algorithms used for the Stokes problem. Recent improvements concerning the optimization of finite element calculations are also detailed. The second part deals with the modelling of the thermal boundary layer used to simulate walls with fixed temperature in turbulent flows. The differences with other modelling suggested in the literature are discussed. The last part presents some applications. EDF is involved in the conception of heating or cooling systems and numerical methods constitute a very useful tool to study the movements of air in habitations. The calculations are validated by comparisons with measurements.
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  • 59
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 493-506 
    ISSN: 0271-2091
    Keywords: finite element method ; mould filling ; explicit Taylor-Galerkin ; pseudo-concentration ; interface elements ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A model for simulating the process of mould filling in castings is presented. Many defects in a casting have their origins at the filling stage. Numerical simulation of this process can be of immense practical benefit to the foundry industry, however a rigorous analysis of this process must model a wide range of complex physical phenomena. In order to contain the costs and complexity that would be necessary for such a model, certain simplifying assumptions have been made. These assumptions limit the scope of this model to only predicting realistic thermal fields during the filling process.A laminar regime has been assumed for the flow field, which is obtained by solving the incompressible Navier-Stokes equations using a velocity-pressure segregated semi-implicit finite element method. The free metal surface is predicted by advecting a pseudo-concentration function via the computed flow field. This involves an explicit finite element solution of a pure advection equation. The thermal field is calculated by solving the convective-diffusive energy equation by an explicit finite element method using the computed flow field and the location of the free surface. All the advection terms are discretized using a Taylor-Galerkin method. The interface between the metal and mould is modelled using special interface elements.The model is demonstrated by solving practical example problems. The results show that a sharp thermal front is maintained during the course of filling without excessive diffusion. The heat diffusion in the mould can be controlled by varying the metal mould heat transfer coefficient.
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  • 60
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 599-601 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 61
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 91-92 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 62
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 93-111 
    ISSN: 0271-2091
    Keywords: smallest drag ; first-order necessary condition ; second-order necessary condition ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The problem of finding the shape of a body with smallest drag in a flow governed by the two-dimensional steady Navier-Stokes equations is considered. The flow is expressed in terms of a streamfunction which satisfies a fourth-order partial differential equation with the biharmonic operator as principal part. Using the adjoint variable approach, both the first- and second-order necessary conditions for the shape with smallest drag are obtained. An algorithm for the calculation of the optimal shape is proposed in which the first variations of solutions of the direct and adjoint problems are incorporated. Numerical examples show that the algorithm can produce the optimal shape successfully.
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  • 63
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 129-139 
    ISSN: 0271-2091
    Keywords: numerical technique ; boundary layer equations ; reacting flow ; full coupling ; finite rate chemistry effects ; thermal radiation effects ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A new numerical scheme for reacting axisymmetric jet flows formed between a fuel jet and co-flowing air has been developed. The model is mathematically described by a set of non-linear parabolic partial differential equations in two space dimensions, i.e. the boundary layer equations. The numerical scheme that the programme uses for solving the fully coupled conservation equations of mass, momentum, energy and species is a generaliztion of the discretization technique recently developed by Villasenor (J. Math. Comput. Simul., 36, 203-208 (1994)). Chemical production (and destruction) of the species is allowed to occur through N elementary reversible (or irreversible) reactions involving k species, although in the present model the reaction rates are evaluated with a simplified kinetic mechanism for a one-step global reaction. Thermal radiation is considered assuming an optically thin limit and adopting the grey medium approximation. Allowances are made for natural convection effects and variable thermodynamic and molecular transport properties. The performance of the model in solving the coupled aerodynamic and finite rate chemistry effects is tested by comparing model predictions with experimental data of Mitchell et al. (Combust. Flame, 37, 227-244 (1980)) for a buoyant, laminar, diffusion axisymmetric methane-air flame.
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  • 64
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 155-180 
    ISSN: 0271-2091
    Keywords: computational fluid dynamics ; finite-difference method ; Navier-Stokes equations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The disarrangement of a perturbed lattice of vortices was studied numerically. The basic state is an exponentially decaying, exact solution of the Navier-Stokes equations. Square arrays of vortices with even numbers of vortex cells along each side were perturbed and their evolution was investigated. Whether the energy in the perturbation grows somewhat before it decays or decays monotonically depends on the initial strength of the vortices of the basic state, the extent of lateral confinement and the structure of the perturbation. The critical condition for temporally local instability, i.e. the critical amplitude of the basic state that must be exceeded to allow energy transfer from the basic state to the perturbation, is discussed. In the strongly confined case of a square lattice of four vortices the appearance of enchancement of global rotation is the result of energy transfer from the basic state to a temporally local unstable mode. Energy is transferred from the basic state to larger-scaled structures (inverse cascade) only if the scales of the larger structures are inherently contained in the initial structure of the perturbation. The initial structure of the double array of vortices is not maintained except for a very special form of perturbation. The facts that large scales decay more slowly than small scales and that, when non-linearities are sufficiently strong, energy is transferred from one scale to another explain the differences in the disarrangement process for different initial strengths of the vortices of the basic state. The stronger vortices, i.e. the vortices perturbed in a manner that increases their strength, tend to dominate the weaker vortices. The pairing and subsequent merging (or capture) of vortices of like sense into larger-scale vortices are described in terms of peaks in the evolution of the square root of the palinstrophy divided by the enstrophy.
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 369-370 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 66
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 401-411 
    ISSN: 0271-2091
    Keywords: unsteady incompressible flow ; vorticity-velocity formulation ; numerical simulation ; staggered grid ; spherical Couette flow ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A new numerical method for solving the axisymmetric unsteady incompressible Navier-Stokes equations using vorticity-velocity variables and a staggered grid is presented. The solution is advanced in time with an explicit two-stage Runge-Kutta method. At each stage a vector Poisson equation for velocity is solved. Some important aspects of staggering of the variable location, divergence-free correction to the velocity field by means of a suitably chosen scalar potential and numerical treatment of the vorticity boundary condition are examined. The axisymmetric spherical Couette flow between two concentric differentially rotating spheres is computed as an initial value problem. Comparison of the computational results using a staggered grid with those using a non-staggered grid shows that the staggered grid is superior to the non-staggered grid. The computed scenario of the transition from zero-vortex to two-vortex flow at moderate Reynolds number agrees with that simulated using a pseudospectral method, thus validating the temporal accuracy of our method.
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 1315-1336 
    ISSN: 0271-2091
    Keywords: numerical wave tank ; multi-subdomain approach ; non-linear water waves ; wave breaking ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: An efficient 2D non-linear numerical wave tank called LONGTANK has been developed based on a multi-subdomain (MSD) approach combined with the conventional boundary element method (BEM). The multi-subdomain approach aims at optimized matrix diagonalization, thus minimizing the computing time and reserved storage. The CPU per time step in LONGTANK simulation is found to increase only linearly with the number of surface nodes, which makes LONGTANK highly efficient especially when simulating long-time wave evolutions in space.Appropriate treatment of special points on the boundary ensures high resolution in LONGTANK simulation beyond initial deformation and breaking, which allows detailed study of breaking criterion, breaker morphology, breaking dissipation, vorticity generation, etc.Detailed numerical implementation has been given with demonstration of LONGTANK simulations.
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 1381-1382 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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    International Journal for Numerical Methods in Fluids 21 (1995) 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 571-590 
    ISSN: 0271-2091
    Keywords: CDF ; predictions ; laser Doppler anemometry ; inlet port ; cylinder ; turbulence ; steady flow ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper presents a combined experimental and computational study of the steady flow through an internal combustion engine inlet port. The port was of generic design with a straight centreline. The three-dimensional velocity and turbulence fields in the port and cylinder were simulated using a computational fluid dynamics programme. Laser sheet flow visualization and laser Doppler anemometry were also employed to investigate the flows and assess the predictions. The results show that a large-scale flow structure is created in the cylinder by the inlet jet and its interaction with the valve and cylinder walls. Both predictions and measurements show that the flow is strongly dependent on the valve lift but is not affected by the flow rate. Comparisons of the numerical predictions with the experimental data indicated that the mean flow features are accurately predicted in many parts of the flow field; some discrepancies are evident and stem primarily from the failure of the simulation to predict a small recirculation region in the port which affects the trajectory of the annular jet entering the cylinder. Calculations were also made without modelling the port shape by using simplified inlet conditions upstream of the valve seat. It was found that this approximation can provide a reasonable, albeit less accurate, description of the flow, but modelling of the port shape is necessary for accurate flow predictions.
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    International Journal for Numerical Methods in Fluids 20 (1995), S. 831-851 
    ISSN: 0271-2091
    Keywords: error estimation ; adaptivity ; hp-methods ; Navier-Stokes ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Recently, a rigorous a posteriori error estimate, based on the element residual method, for the steady-state Navier-Stokes equations has been derived. In this paper, by using this error estimate, we construct an hp adaptive strategy to minimize the total computation costs while achieving a targeted accuracy for steady incompressible viscous flow problems. The basic hp adaptive strategy is to solve the approximate problem in three consecutive stages corresponding to three different meshes, i.e. an initial mesh, an intermediate adaptive h-mesh, and a final adaptive hp mesh. Our numerical result shows that the three-step hp adaptive strategy for the incompressible flow problems indeed provides an accurate approximate solution while keeping the computational costs under control.
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 697-698 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 699-722 
    ISSN: 0271-2091
    Keywords: domain decomposition ; free-surface ; ship flow ; viscous flow ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: An application of multidomain decomposition to the computation of the steady free surface flow past a ship hull is presented. Viscous effects are taken into account in the neighbourhood of solid walls and in the wake by the Reynolds averaged Navier-Stokes equations, whereas the assumption of irrotationality in the external flow allows a description by a potential model. Free surface boundary conditions have been implemented in a linearized form at the undisturbed waterplane. Suitable matching conditions are enforced at the interface between the viscous and the potential regions. The numerical results obtained for two merchant ship forms (the HSVA tanker and the Series 60 hull) are compared with experimental data available in the literature.
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 763-780 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper describes a calculation technique to determine the linear instability characteristics of jets of arbitrary exit geometry. In particular, elliptic and rectangular jets are considered. The numerical procedure involves both a conformal transformation between the computational domain and the physical plane and a solution of the transformed stability equation in the computational domain. Modern, efficient, conformal mappings are used for both simply and doubly connected domains. The numerical solution is based on a hybrid finite difference/pseudospectral discretization of the stability equation. The technique is validated by comparison with previous stability calculations for circular and elliptic jets. Calculations are performed for the stability characteristics of elliptic and rectangular jets of aspect ratio 2:1. Growth rates, phase velocities, and pressure eigenfunctions are presented.
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  • 75
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    International Journal for Numerical Methods in Fluids 21 (1995), S. iii 
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    Keywords: Engineering ; Engineering General
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 76
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 837-856 
    ISSN: 0271-2091
    Keywords: stabilized finite elements ; projection method ; approximate projections ; equal-order interpolation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In an attempt to overcome some of the well-known ‘problems’ with the Q1P0 element, we have devised two ‘stabilized’ versions of the Q1Q1 element, one based on a semi-implicit approximate projection method and the other based on a simple forward Euler technique. While neither one conserves mass in the most desirable manner, both generate a velocity field that is usually ‘close enough’ to divergence-free. After attempting to analyse the two algorithms, each of which includes some ad hoc ‘enhancements’, we present some numerical results to show that they both seem to work well enough. Finally, we point out that any projection method that uses a ‘pressure correction’ approach is inherently limited to time-accurate simulations and, even if treated fully implicitly, is inappropriate for seeking steady states via large time steps.
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  • 77
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    Keywords: wavelet ; multiple scale methods ; optimal dilation parameter ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Multiple scale methods based on reproducing kernel and wavelet analysis are developed. These permit the response of a system to be separated into different scales. These scales can be either the wave numbers corresponding to spatial variables or the frequencies corresponding to temporal variables, and each scale response can be examined separately. This complete characterization of the unknown response is performed through the integral window transform, and a space-scale and time-frequency localization process is achieved by dilating the flexible multiple scale window function. An error estimation technique based on this decomposition algorithm is developed which is especially useful for local mesh refinement and convergence studies. This flexible space-scale window function can be constructed to resemble the well-known unstructured multigrid and hp-adaptive finite element methods. However, the multiple scale adaptive refinements are performed simply by inserting nodes into the highest wavelet scale solution region and at the same time narrowing the window function. Hence hp-like adaptive refinements can be performed without a mesh. An energy error ratio parameter is also introduced as a measure of aliasing error, and critical dilation parameters are determined for a class of spline window functions to obtain optimal accuracy. This optimal dilation parameter dictates the number of nodes covered under the support of a given window function. Numerical examples, which include the Helmholtz equation and the 1D and 2D advection-diffusion equations, are presented to illustrate the high accuracy of the methods using the optimal dilation parameter, the concept of multiresolution analysis and the meshless unstructured adaptive refinements.
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 955-966 
    ISSN: 0271-2091
    Keywords: Laplace transform ; combined method ; transient problem ; chemical reaction ; convective diffusion ; infinite region ; finite element method ; boundary element method ; coupling method ; unsteady problem ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A numerical method for solving the problem of transient convective diffusion with a first-order chemical reaction is presented in this paper. The method is applicable over an infinite region. For steady problems the combined method of finite and boundary elements is recognized as a successful numerical technique for dealing with an infinite region. The present method is also useful in transient problems. In order to formulate the combined method for transient problems, we have developed a new method. In this paper the Laplace transform method incorporating the combined finite and boundary element methods will be considered. This transformation, holding complex values, transforms the transient problem into a steady state form. We also consider the present numerical solution which is obtained by using the numerical inverse Laplace transform as presented by Hosono. In numerical experiments the present method gives us an extremely accurate solution.
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 1007-1014 
    ISSN: 0271-2091
    Keywords: finite element ; massively parallel ; coupled flow ; baroclinic annulus waves ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Coupled, three-dimensional, time-dependent, incompressible flows in a differentially heated, rotating annulus are simulated using a parallel implementation of the Galerkin finite element method on the Connection Machine 5 (CM-5) supercomputer. The development of baroclinic annulus waves is computed and found to be consistent with previous experimental reseults. The implementation of a repeated spectral bisection element-partitioning technique significantly increases the computation speed over a strategy which randomly maps elements to processors, yielding sustained calculation rates of 8.1 GFLOPS on 512 processors of the CM-5.
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 141-153 
    ISSN: 0271-2091
    Keywords: incompressible flow ; artificial compressibility ; artificial bulk viscosity ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Peyret (J. Fluid Mech., 78, 49-63 (1976)) and others have described artificial compressibility iteration schemes for solving implicit time discretizations of the unsteady incompressible Navier-Stokes equations. Such schemes solve the implicit equations by introduing derivatives with respect to a pseudo-time variable τ and marching out to a steady state in τ. The pseudo-time evolution equation for the pressure p takes the form ∂p/∂ = -a2∂∇.u, where a is an artificial compressibility parameter and u is the fluid velocity vector. We present a new scheme of this type in which convergence is accelerated by a new procedure for setting a and by introducing an artificial bulk viscosity b into the momentum equation. This scheme is used to solve the non-linear equations resulting from a fully implicit time differencing scheme for unsteady incompressible flow. We find that the best values of a and b are generally quite different from those in the analogous scheme for steady flow (J. D. Ramshaw and V. A. Mousseau, Comput. Fluids, 18, 361-367 (1990)), owing to the previously unrecognized fact that the character of the system is profoundly altered by the pressence of the physical time derivative terms. In particular, a Fourier dispersion analysis shows that a no longer has the significance of a wave speed for finite values of the physical time step δt,. Inded, if on sets a ˜ |u| as usual, the artificial sound waves cease to exist when δt is small and this adversely affects the iteration convergence rate. Approximate analytical expressions for a and b are proposed and the benefits of their use relative to the conventional values a ∼ |u| and b = 0 are illustrated in simple test calculations.
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    International Journal for Numerical Methods in Fluids 21 (1995) 
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    Keywords: Engineering ; Engineering General
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 205-222 
    ISSN: 0271-2091
    Keywords: two-phase ; Van Leer ; convective transport ; volume fractions ; momentum ; interface tracking ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The Van Leer method for the computation of convective fluxes is extended to two-phase flow. By preventing spurious undershoots and overshoots, the scheme preserves physical realism while maintaining high-order accuracy. This is particulary important for two-phase flows, since phase exchange terms are typically a function of volume fraction products and numerical diffusion can incorrectly mix the two phases. The scheme described here is constructed to guarantee that the sum of the volume fractions is always unity and that the volume fractions are always greater than or equal to zero. Various test problems are computed to demonstrate the accuracy of the method and to show how the scheme might be incorporated in existing computational methods. In addition to multiphase flow applications, setting equal phase velocities results in a volume marker scheme that is well suited to single-phase interface tracking problems.
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 237-251 
    ISSN: 0271-2091
    Keywords: finite volume ; multigrid ; unsteady flow ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper presents results of the numerical study of a piston-driven unsteady flow in a pipe with sudden expansion. The piston closes the larger-diameter pipe and moves between two limiting positions with strong acceleration or deceleration at the beginning and end of each stroke and constant velocity in between. The piston velocity in the exhaust stroke is about four times higher than in the intake stroke. Periodic piston movement in this fashion creates a complex unsteady flow between the piston head and the plane of sudden expansion. The numerical method is implicit and of finite volume type, using a moving grid and a collocated arrangement of variables. Second-order spatial discretization, fine grids and a multigrid solution method were used to ensure high accuracy and good efficiency. Spatial and temporal discretization errors were of the order of 1% and 0.1% respectively. The features of the flow are discussed and the velocity profiles are compared with experimental data, showing good qualitative and quantitative agreement.
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  • 84
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 253-278 
    ISSN: 0271-2091
    Keywords: volcanic conduits ; homogeneous flow ; exsolution ; total-variation-diminishing techniques ; method of characteristics ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A one-dimensional, time-dependent, isothermal, homogeneous, two-phase flow model was developed to study magma ascent in volcanic conduits. The physical modeling equations were numerically solved by means of a TVD (total variation diminishing) predictor-corrector procedure and by means of a predictor-corrector technique based on the method of characteristics. The results from the transient model were verified with an analytical solution for wave propagation in conduits without friction and gravitational effects. The numerical solutions were also compared with those of a steady-state, homogeneous, two-phase model for basaltic and rhyolitic magma ascents in the fissures and circular conduits of Vesuvius and Mt St. Helens. An application of the model to magma decompression in conduits indicates very short times for gas exsolution, fragmentation, and shock wave propagation, implying that the modelling of gas exsolution should involve non-equilibrium kinetics effects. Future coupling of the transient magma ascent model with magma chamber and pyroclastic dispersion models should allow for more realistic simulations of the time-dependent behavior of real volcanic eruptions.
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  • 85
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 967-972 
    ISSN: 0271-2091
    Keywords: lattice gas model ; cellular automaton ; shear layer ; diffusion ; Kelvin-Helmholtz instability ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The ‘two-colour lattice gas model’ is applied to the analysis of shear layers between two parallel flows with different velocities U1 and U2. Two cases, (a) U1 = 0.4, U2 = 0.2 and (b) U1 = 0.4, U2 = 0.0, are calculated and compared with the theoretical solutions. We obtain good agreement between theory and calculations in the velocity profiles of the shear layers. It is found that this model can simulate complicated physical phenomena of shear layers at the microscopic level.
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  • 86
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 973-979 
    ISSN: 0271-2091
    Keywords: finite element method ; transient flow ; power-law fluid ; extrudate swell ; marker particles ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A simple extrusion process for Newtonian and power-law fluids is analysed. Marker particles are introduced to analyse the fluid flow motions. Area co-ordinates of six-node triangular element are used to determine the marker position in the element. With this element, the solution algorithm becomes simple compared with the one using the linear triangular element. The differences in flow and swell patterns between the two fluids are described.
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  • 87
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 1015-1016 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 88
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 1017-1039 
    ISSN: 0271-2091
    Keywords: turbulence models ; flux-difference splitting ; multigrid method ; transonic turbulent flow ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this paper Roe's flux-difference splitting is applied for the solution of Reynolds-averaged Navier-Stokes equations. Turbulence is modelled using a low-Reynolds number form of the k-∊ tubulence model. The coupling between the turbulence kinetic energy equation and the inviscid part of the flow equations is taken into account. The equations are solved with a diagonally dominant alternating direction implicit (DDADI) factorized implicit time integration method. A multigrid algorithm is used to accelerate the convergence. To improve the stability some modifications are needed in comparison with the application of an algebraic turbulence model. The developed method is applied to three different test cases. These cases show the efficiency of the algorithm, but the results are only marginally better than those obtained with algebraic models.
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  • 89
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 1067-1086 
    ISSN: 0271-2091
    Keywords: laminar flows ; incompressible flows ; pressure correction ; Krylov subspace methods ; approximate factorization ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A segregated algorithm for the solution of laminar incompressible, two- and three-dimensional flow problems is presented. This algorithm employs the successive solution of the momentum and continuity equations by means of a decoupled implicit solution method. The inversion of the coefficient matrix which is common for all momentum equations is carried out through an approximate factorization in upper and lower triangular matrices. The divergence-free velocity constraint is satisfied by formulating and solving a pressure correction equation. For the latter a combined application of a preconditioning technique and a Krylov subspace method is employed and proved more effecient than the approximate factorization method. The method exhibits a monotonic convergence, it is not costly in CPU time per iteration and provides accurate solutions which are independent of the underrelaxation parameter used in the momentum equations. Results are presented in two- and three-dimensional flow problems.
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  • 90
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 1087-1107 
    ISSN: 0271-2091
    Keywords: two-layer ; finite difference ; time splitting ; orthogonal curvilinear co-ordinates ; grid ‘block’ ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A new two-layer, two-dimensional mathematical model employing a finite difference method based on numerically generated boundary-fitted orthogonal co-ordinates and a grid ‘block’ technique for unsteady boundary problems is developed which can be used to simulate flows with density stratification in a natural water-body with complicated topography. In the model the turbulent exchange across the interface is treated empirically and a time-splitting finite difference method with two fractional steps is employed to solve the governing equations. The model is calibrated and verified by comparing the computational results with data measured in Tolo Harbour, Hong Kong. The simulation results mimie the field measurements very closely. The computation shows that the model reproduces the two-layer, two-dimensional tidal flow with density stratification in Tolo Harbour very well. The computed velocity hodographs show that the tidal circulations at various positions in each layer have different patterns and that the features of the patterns are independent of the tidal type except for their scales. The computed Lagrangian pathlines show that the tidal excursion is dependent on the tidal type, especially in the inner harbour and side-coves.
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  • 91
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 1137-1151 
    ISSN: 0271-2091
    Keywords: transient planar flow ; viscoelastic material ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this study, we examine the numerical simulation of transient viscoelastic flows with two moving free surfaces. A modified Galerkin finite element method is implemented to the two-dimensional non-steady motion of the fluid of the Oldroyd-B type. The fluid is initially placed between two parallel plates and bounded by two straight free boundaries. In this Lagrangian finite element method, the spatial mesh deforms in time along with the moving free boundaries. The unknown shape of the free surfaces is determined with the flow field u, v, τ, p by the deformable finite element method, combined with a predictor-corrector scheme in an uncoupled fashion. The moving free surfaces and fluid motion of both Newtonian and non-Newtonian flows are investigated. The results include the influence of surface tension, fluid inertia and elasticity.
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  • 92
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    International Journal for Numerical Methods in Fluids 21 (1995), S. 1171-1200 
    ISSN: 0271-2091
    Keywords: implicit schemes ; non-symmetric matrices ; iterative procedures ; relaxation methods ; gradient methods ; quasinewton methods ; convection-diffusion equation ; Euler equation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Various tests have been carried out in order to compare the performances of several methods used to solve the non-symmetric linear systems of equations arising from implicit discretizations of CFD problems, namely the scalar advection-diffusion equation and the compressible Euler equations. The iterative schemes under consideration belong to three families of algorithms: relaxation (Jacobi and Gauss-Seidel), gradient and Newton methods. Two gradient methods have been selected: a Krylov subspace iteration method (GMRES) and a non-symmetric extension of the conjugate gradient method (CGS). Finally, a quasi-Newton method has also been considered (Broyden). The aim of this paper is to provide indications of which appears to be the most adequate method according to the particular circumstances as well as to discuss the implementation aspects of each scheme.
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  • 93
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 515-548 
    ISSN: 0271-2091
    Keywords: incompressible ; Navier-Stokes ; contravariant velocities ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: To analyse an incompressible Navier-Stokes flow problem in a boundary- fitted curvilinear co-ordinate system is definitely not a trivial task. In the primitive variable formulation, choices between working variables and their storage points have to be made judiciously. The present work engages contravariant velocity components and scalar pressure which stagger each other in the mesh to prevent even-odd pressure oscillations from emerging. Now that smoothness of the pressure field is attainable, the remaining task is to ensure a discrete divergence-free velocity field for an incompressible flow simulation. Aside from the flux discretizations, the indispensable metric tensors, Jacobian and Christoffel symbols in the transformed equations should be approximated with care. The guiding idea is to get the property of geometric identity pertaining to these grid-sensitive discretizations. In addition, how to maintain the revertible one-to-one equivalence at the discrete level between primitive and contravariant velocities is another theme in the present staggered formulation. A semi-implicit segregated solution algorithm felicitous for a large-scale flow simulation was utilized to solve the entire set of basic equations iteratively. Also of note is that the present segregated solution algorithm has the virtue of requiring no user-specified relaxation parameters for speeding up the satisfaction of incompressibility in an optimal sense. Three benchmark problems, including an analytic problem, were investigated to justify the capability of the present formulation in handling problems with complex geometry. The test cases considered and the results obtained herein make a useful contribution in solving problems subsuming cells with arbitrary shapes in a boundary-fitted grid system.
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  • 94
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 619-641 
    ISSN: 0271-2091
    Keywords: convective transport ; monotonicity ; finite volume ; boundary-fitted co-ordinates ; turbulence modelling ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A formally third-order accurate finite volume upwind scheme which preserves monotonicity is constructed. It is based on a third-order polynomial interpolant in Leonard's normalized variable space. A flux limiter is derived using the fact that there exists a one-to-one map between normalized variable and TVD spaces. This scheme, which is relatively simple and quite compact, is implemented in a staggered general co-ordinates finite volume algorithm including the standard k-ε model and applied to the turbulence transport equations. A number of test problems demonstrate the utility of the proposed scheme. It is shown that in cases where turbulence convection is dominant, the application of a higher-order monotone convection scheme to the turbulence equations leads to results which are more accurate than those obtained using the first-order upwind scheme.
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  • 95
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 673-688 
    ISSN: 0271-2091
    Keywords: Navier-Stokes equations ; projection methods ; operator splitting ; spectral element methods ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: An approximate projection scheme based on the pressure correction method is proposed to solve the Navier-Stokes equations for incompressible flow. The algorithm is applied to the continuous equations; however, there are no problems concerning the choice of boundary conditions of the pressure step. The resulting velocity and pressure are consistent with the original system. For the spatial discretization a high-order spectral element method is chosen. The high-order accuracy allows the use of a diagonal mass matrix, resulting in a very efficient algorithm. The properties of the scheme are extensively tested by means of an analytical test example. The scheme is further validated by simulating the laminar flow over a backward-facing step.
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  • 96
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    International Journal for Numerical Methods in Fluids 22 (1996) 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 97
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 755-770 
    ISSN: 0271-2091
    Keywords: Stokes ; multigrid ; Krylov subspace ; conjugate gradient ; conjugate residual ; Uzawa ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Discretization of the Stokes equations produces a symmetric indefinite system of linear equations. For stable discretizations a variety of numerical methods have been proposed that have rates of convergence independent of the mesh size used in the discretization. In this paper we compare the performance of four such methods, namely variants of the Uzawa, preconditioned conjugate gradient, preconditioned conjugate residual and multigrid methods, for solving several two-dimensional model problems. The results indicate that multigrid with smoothing based on incomplete factorization is more efficient than the other methods, but typically by no more than a factor of two. The conjugate residual method has the advantage of being independent of iteration parameters.
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  • 98
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 799-810 
    ISSN: 0271-2091
    Keywords: jets ; jet impingement ; turbulence ; k-ε model ; finite volume method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper reports numerical modelling of impinging jet flows using Rodi and Malin corrections to the k-ε turbulence model, carried out using the PHOENICS finite volume code. Axisymmetric calculations were performed on single round free jets and impinging jets and the effects of pressure ratio, height and nozzle exit velocity profile were investigated numerically. It was found that both the Rodi and Malin corrections tend to improve the prediction of the hydrodynamic field of free and impinging jets but still leave significant errors in the predicted wall jet growth. These numerical experiments suggest that conditions before impingement significantly affect radial wall jet development, primarily by changing the wall jet's initial thickness.
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  • 99
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 771-798 
    ISSN: 0271-2091
    Keywords: curved pipe flow ; variable cross-section ; secondary flow ; artery ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper is concerned with steady, laminar flow of an incompressible Newtonian fluid in curved pipes of non-uniform cross-section. During the past decade a number of numerical solutions for flow in curved pipes have been obtained using progressively improved computational methods and technology; see e.g. Soh and Berger (Int. j. numer. methods fluids, 7, 733-755 (1987)) and Green et al. (Phil. Trans. R. Soc. Lond. A, 342, 543-572 (1993)) for relevant references. These results have been confined mainly to fully developed flow in pipes of constant cross-section. The present study deals with curved pipes of variable cross-section in which the velocity field is necessarily a function of the axial location along the pipe centreline in addition to the two cross-sectional co-ordinates. We use the finite difference method on a staggered grid with Newton's method to solve the Navier-Stokes equations. Results are calculated and presented for non-uniform pipe geometries with curvature ratios of 0ċ01 and 0ċ1. The velocity field for flow through curved pipes of non-uniform cross-section is compared with the corresponding results for flow through straight pipes of non-uniform radius and curved pipes of uniform radius, revealing important qualitative differences. The basic developments presented are applicable to a variety of flows in pipes, including those in arteries and piping systems.
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  • 100
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 835-849 
    ISSN: 0271-2091
    Keywords: non-linear first-order hyperbolic system ; collocation method ; upwinding ; thermal pipeline simulation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Simulating thermal effects in pipeline flow involves solving a coupled non-linear system of first-order hyperbolic equations. The advection term has two large eigenvalues of opposite signs, corresponding to the propagation of high-speed sound waves, and one eigenvalue close to or even equal to zero, representing the much slower fluid flow velocity, which transports temperature. Standard collocation methods work well for isothermal flow in pipelines, but the stagnating eigenvalue causes difficulties when thermal effects are included. In a companion paper we formulate and analyse a new numerical method for the non-linear system which arises in thermal modelling. The new method applies to general coupled systems of non-linear first-order hyperbolic partial differential equations with one degenerate eigenvalue. In the present paper we focus on a linearized constant coefficient form of the thermal flow equations. This substantially simplifies presentation of the error analysis for the numerical scheme. We also include numerical results for the method applied to the fully non-linear system. Both the error analysis and the numerical experiments show that the difficulties that come from the application of standard collocation can be overcome by using upwinded piecewise constant functions for the degenerate component of the solution.
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